Serviceability limit statesare concerned with ensuring that the deformations of a structure
due to ground movements below the foundations do not damage the appearance or reduce
the useful life of the structure, or cause damage to finishes, non-structural elements,
machinery or other installations in the structure.
EC7 requires structures and their foundations to have sufficient durabilityto resist
weakening from attack by substances in the ground or the environment.
The design methods using EC7 can be advantageous compared to permissible stress methods
when designing structures using BS8110 (Code of practice structural concrete) or BS 5950
(structural steelwork in buildings), or BS5400 (bridges), which are all limit state codes, in that
difficulty is avoided in achieving compatibility between them and the foundation code BS 8004
which is based on permissible stresses. When the use of BS8004 for the foundations in con-
junction with limit state codes for the superstructure cannot be avoided, the superstructure
designer should specify clearly whether or not the loads applied to the foundations are factored
or unfactored total loads, or are dead loads combined with factored imposed loading.
In addition to EC7, Eurocodes relevant to pile foundation design are the following:
BSEN 1990 Basis of structural design
BSEN 1991 Action on structures
BSEN 1992 Design of concrete structures
BSEN 1993 Design of steel structures
BSEN 1994 Design of composite concrete and steel structures
BSEN 1995 Design of timber structures
BSEN 1996 Design of masonry structures
BSEN 1998 Design of structures for earthquake resistance
BSEN 1999 Design of aluminium structures
As a preliminary EC7 requires the structure to be considered in three categories of risk
from the foundation aspect. Geotechnical Category 1 covers structures having negligible
risk of failure or damage due to ground movements, or where enough is known about the
ground conditions to adopt a routine method of design, provided that there are no risk problems
associated with excavation below groundwater level.
Category 2 includes conventional structures and their foundations with no exceptional
risk or difficult ground or loading conditions. Structures requiring piling come into this
category provided that there is adequate geotechnical data based on routine methods of
ground investigation.
Category 3 applies to all categories not coming within the scope of 1 and 2. It includes very
large or unusual structures and those involving abnormal risks or exceptionally difficult
ground or loading conditions, also structures in highly seismic areas and areas of site
instability. EC7 (Clause 2.2) lists 15 geological and environmental features which need to be
considered generally in foundation design. All of these are relevant to piled foundations for
which the code prescribes three basic approaches to design. These are the following:
Static load tests
Empirical or analytical calculations
Dynamic load tests.
Design by prescriptionand by the observational methodare also referred to in the general
part of the code. The prescriptive method applies to the tables of allowable bearing pressures
144 Resistance of piles to compressive loads